A team of infiltrators from the triad penetrated the police force. However, the police also has sent a team of undercover agents to infiltrate the triad. Ten years later, they are still undercover, but their minds have been twisted by the temptation of power, authority and money — and nobody is certain about their original roles anymore. Both groups learn that they have been infiltrated and want to ferret out the moles. Each mole has a secret code to lock their identity file, and once the code is cracked their identiIty is fully revealed. The battle of wits starts now. Either exposing the enemy or taking the chance to change the identity for good can save their lives as long as nobody knows who is who!

Internal Affairs is an intense elimination game between infiltrators from both the Triad and the Police Force Infiltrator. Each player has a set of secret ID cards which determine that player's allegiance. Each player also has a secret code, which when cracked reveals the player's real ID. At the beginning of the game, each player has five code cards and chooses three of them to be the secret code that locks the identity file. During their turn, players try to crack other players' codes to find out who is who and get their team to victory. Due to action cards, though, ID cards may be passed from player to player and this may change each player's allegiance. Players must be quick to win, as otherwise they may end up in the losing team when they least expect it.